Hotbar bonding machine

I would like to make a hotbar machine( used for hotbar soldering).
As far as I know hotbar uses a thermode that is heated up to about 250 degrees.
For heating it uses a kind of resistive heating.
It means I should use a transformator that has about 300A ( short circuit current)and only about 4V on secondary .
But a such transformator is rather large, so I would need a
Switched-mode power supply
Does anyone have any schematic for such strong power supply?
Or a different idea how to reach such current output?
Thank you.

I don't know the maximum current from my modified microwave transformer, but you can get the transformers in the 1500W range. Remove the secondary and control coil and wrap a few turns of #4 welding cable in the space you create. It may work for your needs, if your use will not be continuous. I made one for spot welding. I use a simple zero-crossing switch to time a dozen cycles or so for welding. I think that would be a lot cheaper in the long run and easier than a 300A SM power supply to design and build. I don't consider that transformer very big in comparison to the transformers in a 300A welder. A local shop gave me the starting transformer from a broken microwave.

John

Jp's idea is a good one, if your new to switchers building a 1.5kw one is not a good idea.
Mot's are a cheap easy source of high current ac.

Here' s a picture of my modified MOT. The projected face is 5" x 5" square.


John

300A is a scary amount of current. Could quickly make for a bad day. Safety, Safety, Safety...

Here is one I Made, for Really High Current at a LOW Voltage.

It is 1/2 Inch Copper Pipe, Flattened, Bent and Soldered Together, to wrap around Core.

A TRIAC Circuit on the Primary can control the Output.

Jp, your trans is shown with the shunts still in place, have you tried it with them removed, the shunts are there to increase the impedance of the trans so that it matches the magnetron, if your driving a resistive load then without them you'll get more amps.
A mot is intenitonally very leaky magnetic field wise, thats why all the e's and i's are aligned, also they are designed to run loaded, with no load te core will saturate and the primary will overheat, not a problem for a spotter.

Jane, for 300a at 4v you'll need a commercial microwave transformer, as that is a lot of power, 1.6kw commercial ones are around, also if you use a triac circuit use one designed for use with a transformer, light dimmers produce dc offset which will heat the primary even more.

Nice work gaz, did you squash some copper tube, or is that busbar.

It is a DPC YSH200 Y800TC transformer -- a freebie from a local repair shop. I did not remove the shunts. It gave plenty of power for spot welding small SS tubing (up to about 0.188"), but I wanted to spot weld battery tabs too and was concerned about the wide heat zone. So, I built a CD welder and haven't played with the MOT since. If I ever get back to it, I will remember your advice.

John

I Flattened 1/2 Inch Diameter, "Copper Water Pipe".
I Don't have any Large Busbar.

Thats a good idea I'll remember that one, a smps car starter is a project I'd like to do.

Thanks for the posts.
I also thought about using an adopted Microwave Oven Transformer ( MOT).
Here are parameters I need to achieve from a such modified transformer.
The secondary will power a soldering tip of size 100 x 20 x 2 mm ( length x height x thicknes).
This tips must reach temperature of about 180° during 10 seconds or sooner
The spot welder works in a way that it is short circuited for very few seconds ( 2 sec or so) , I think.
But my soldering machine( hotbar bonding machine) will need to heat the tip much longer.
At least for about 10 sec in one step.( one bonding)

So,questions are:
Will really be MOT suitable?
Will be necessary SMPS power supply?
What material the soldering tip should be made of?


@chemelec:You say : "A TRIAC Circuit on the Primary can control the Output."
Can you please let me know further details?

Thank you

Hi Jane,

Now, I think I have a better idea of what you want to do. The MOT will work, but since you only need 180°C, I would consider using a soldering gun like this:


I got that gun years ago to work with plastic. (I have always disliked them for real soldering.)

I have made various tips. The folded wire is about 2 mm diameter. I would take a solid piece of copper the size you describe and make a deep notch to fit the gun's holders. Alternatively, braze the copper plate you have to one of the tips, like the one on top.

The more copper you have, the better temp control you will probably get. However, the gun may not be able to heat a full 100mm x 20mm x 2mm plate. If the 100-mm dimension could be reduced to 20 mm or so, then I think it might work.

That gun is rated at 230 W maximum, and the tips get red hot quite quickly.

John

My guess is that a rewound mot could be shorted for 10 secs, probably 3 or 4 times before the windings got mad hot, maybe 5 or 6 with a cooling fan, if you kept the shunts current would be lower but primary heating would also be lower.

A smps you'd need to rectify mains to create a 320v bus, then chop said 320v into high freq ac with a mosfet or igbt, like 40khz, this then goes to a transformer, the o/p of which would have a high current ultrafast rectifier/smoothing cap/smoothing choke, the whole thing being controlled by an smps controller ic such as a uc3842 or sg3525 or similar, for this sort of power forward topology would be suitable.
The tricky part is designing the transformer, working out gate drive, and frequency compensation.
I was going to refer you to a site that shows mains powered smps's however I really dont think you ought to try and build something like this as a first smps project, offline smps's are dangerous.

Jane11 said:

@chemelec:You say : "A TRIAC Circuit on the Primary can control the Output."
Can you please let me know further details?

Thank you

Click to expand...

Most Light Dimmers use an SCR.
These are only good for on-Inductive Loads.

If you get a Light Dimmer that uses a TRIAC instead of a SCR, It is good for Controlling a Transformer.

Thank you for the replies.
chemelec: I am going to use SSR( solid state relay) to control current to the transformer.
dr pepper: Can you please refer the site that shows mains powered smps's, as you mentioned?
jpanhalt: It is an interesting idea to use a soldering gun. But do you think it will still reach about 200°, if I make soldering tip larger?